If the target player is an illegal target by the time Risk Factor tries to resolve, the spell doesn’t resolve. You don’t draw three cards.

10/5/2018

You must still follow any timing restrictions and permissions, including those based on the card’s type. For instance, you can cast a sorcery using jump-start only when you could normally cast a sorcery.

10/5/2018

A spell cast using jump-start will always be exiled afterward, whether it resolves, it’s countered, or it leaves the stack in some other way.

10/5/2018

If an effect allows you to pay an alternative cost rather than a spell’s mana cost, you may pay that alternative cost when you jump-start a spell. You’ll still discard a card as an additional cost to cast it.

10/5/2018

If a card with jump-start is put into your graveyard during your turn, you’ll be able to cast it right away if it’s legal to do so, before an opponent can take any actions.